Vapor phase carbonylation process using group 5 metal promoted iridium catalyst

ABSTRACT

A method for producing esters and carboxylic acids from lower alkyl alcohols, ethers, esters and ester-alcohol reactant mixtures and includes the step of contacting a vaporous mixture of the reactants, carbon monoxide and a halide with a supported catalyst under vapor-phase carbonylation conditions. The catalyst includes iridium and a second metal selected from group 5 (vanadium, niobium, tantalum) metals of the periodic table of elements. Desirably, the iridium and secondary metal are deposited on activated carbon as a support material. In a preferred aspect of the invention, the vapor phase carbonylation process is useful for preparing acetic acid, methyl acetate or a mixture thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for the vapor phasecarbonylation of alkyl alcohols, ethers and ester-alcohol mixtures toproduce esters and carboxylic acids. Particularly, the present inventionrelates to the carbonylation of methanol to produce acetic acid andmethyl acetate. More particularly, the present invention relates to amethod of producing acetic acid and methyl acetate by contactingvaporous reactants with a catalyst. The catalyst includes an effectiveamount of iridium and at least one second metal selected from group 5metals of the periodic table of elements.

2. Background of the Invention

Lower carboxylic acids and esters such as acetic acid and methyl acetatehave been known as industrial chemicals for many years. Acetic acid isused in the manufacture of a variety of intermediary and end-products.For example, an important derivative is vinyl acetate which can be usedas monomer or co-monomer for a variety of polymers. Acetic acid itselfis used as a solvent in the production of terephthalic acid, which iswidely used in the container industry, and particularly in the formationof PET beverage containers.

There has been considerable research activity in the use of metalcatalysts for the carbonylation of lower alkyl alcohols, such asmethanol, and ethers to their corresponding carboxylic acids and esters,as illustrated in equations 1-3 below:

ROH+CO→RCOOH  (1)

2ROH+CO→RCOOR+water  (2)

ROR′+CO→RCOOR  (3)

Carbonylation of methanol is a well known reaction and is typicallycarried out in the liquid phase with a catalyst. A thorough review ofthese commercial processes and other approaches to accomplishing theformation of acetyl from a single carbon source is described by Howardet al. in Catalysis Today, 18 (1993) 325-354. Generally, the liquidphase carbonylation reaction for the preparation of acetic acid usingmethanol is performed using homogeneous catalyst systems comprising aGroup VIII metal and iodine or an iodine-containing compound such ashydrogen iodide and/or methyl iodide. Rhodium is the most common GroupVIII metal catalyst and methyl iodide is the most common promoter. Thesereactions are conducted in the presence of water to preventprecipitation of the catalyst.

U.S. Pat. No. 5,144,068 describes the inclusion of lithium in thecatalyst system which allows the use of less water in the Rh—Ihomogeneous process. Iridium also is an active catalyst for methanolcarbonylation reactions but normally provides reaction rates lower thanthose offered by rhodium catalysts when used under otherwise similarconditions.

U.S. Pat. No. 5,510,524 teaches that the addition of rhenium improvesthe rate and stability of both the Ir—I and Rh—I homogeneous catalystsystems.

European Patent Application EP 0 752 406 A1 teaches that ruthenium,osmium, rhenium, zinc, cadmium, mercury, gallium, indium, or tungstenimprove the rate and stability of the liquid phase Ir—I catalyst system.Generally, the homogeneous carbonylation processes presently being usedto prepare acetic acid provide relatively high production rates andselectivity. However, heterogeneous catalysts offer the potentialadvantages of easier product separation, lower cost materials ofconstruction, facile recycle, and even higher rates.

Schultz, in U.S. Pat. No. 3,689,533, discloses using a supported rhodiumheterogeneous catalyst for the carbonylation of alcohols to formcarboxylic acids in a vapor phase reaction. Schultz further disclosesthe presence of a halide promoter.

Schultz in U.S. Pat. No. 3,717,670 describes a similar supported rhodiumcatalyst in combination with promoters selected from Groups IB, IIIB,IVB, VB, VIB, VIII, lanthanide and actinide elements of the PeriodicTable.

Uhm, in U.S. Pat. No. 5,488,143, describes the use of alkali, alkalineearth or transition metals as promoters for supported rhodium for thehalide-promoted, vapor phase methanol carbonylation reaction. Pimblett,in U.S. Pat. No. 5,258,549, teaches that the combination of rhodium andnickel on a carbon support is more active than either metal by itself.

In addition to the use of iridium as a homogeneous alcohol carbonylationcatalyst, Paulik et al., in U.S. Pat. No. 3,772,380, describe the use ofiridium on an inert support as a catalyst in the vapor phase,halide-promoted, heterogeneous alcohol carbonylation process.

European Patent Applications EP 0 120 631 A1 and EP 0 461 802 A2describe the use of special carbons as supports for single transitionmetal component carbonylation catalysts.

European Patent Application EP 0 759 419 A1 pertains to a process forthe carbonylation of an alcohol and/or a reactive derivative thereof.

EP 0 759 419 A1 discloses a carbonylation process comprising a firstcarbonylation reactor wherein an alcohol is carbonylated in the liquidphase in the presence of a homogeneous catalyst system and the off gasfrom this first reactor is then mixed with additional alcohol and fed toa second reactor containing a supported catalyst. The homogeneouscatalyst system utilized in the first reactor comprises a halogencomponent and a Group VIII metal selected from rhodium and iridium. Whenthe Group VIII metal is iridium, the homogeneous catalyst system alsomay contain an optional co-promoter selected from the group consistingof ruthenium, osmium, rhenium, cadmium, mercury, zinc, indium andgallium. The supported catalyst employed in the second reactor comprisesa Group VIII metal selected from the group consisting of iridium,rhodium, and nickel, and an optional metal promoter on a carbon support.The optional metal promoter may be iron, nickel, lithium and cobalt. Theconditions within the second carbonylation reactor zone are such thatmixed vapor and liquid phases are present in the second reactor. Thepresence of a liquid phase component in the second reactor inevitablyleads to leaching of the active metals from the supported catalystwhich, in turn, results in a substantial decrease in the activity of thecatalyst.

The literature contains several reports of the use of rhodium-containingzeolites as vapor phase alcohol carbonylation catalysts at one barpressure in the presence of halide promoters. The lead references onthis type of catalyst are presented by Maneck et al. in Catalysis Today,3 (1988), 421-429. Gelin et al., in Pure & Appl. Chem., Vol 60, No. 8,(1988) 1315-1320, provide examples of the use of rhodium or iridiumcontained in zeolite as catalysts for the vapor phase carbonylation ofmethanol in the presence of halide promoter. Krzywicki et al., inJournal of Molecular Catalysis, 6 (1979) 431-440, describe the use ofsilica, alumina, silica-alumina and titanium dioxide as supports forrhodium in the halide-promoted vapor phase carbonylation of methanol,but these supports are generally not as efficient as carbon. Luft etal., in U.S. Pat. No. 4,776,987 and in related disclosures, describe theuse of chelating ligands chemically attached to various supports as ameans to attach Group VIII metals to a heterogeneous catalyst for thehalide-promoted vapor phase carbonylation of ethers or esters tocarboxylic anhydrides.

Evans et al., in U.S. Pat. No. 5,185,462, describe heterogeneouscatalysts for halide-promoted vapor phase methanol carbonylation basedon noble metals attached to nitrogen or phosphorus ligands attached toan oxide support.

Panster et al., in U.S. Pat. No. 4,845,163, describe the use ofrhodium-containing organopolysiloxane-ammonium compounds asheterogeneous catalysts for the halide-promoted liquid phasecarbonylation of alcohols.

Drago et al., in U.S. Pat. No. 4,417,077, describe the use of anionexchange resins bonded to anionic forms of a single transition metal ascatalysts for a number of carbonylation reactions including thehalide-promoted carbonylation of methanol. Although supported ligandsand anion exchange resins may be of some use for immobilizing metals inliquid phase carbonylation reactions, in general, the use of supportedligands and anion exchange resins offer no advantage in the vapor phasecarbonylation of alcohols compared to the use of the carbon as a supportfor the active metal component.

Nickel on activated carbon has been studied as a heterogeneous catalystfor the halide-promoted vapor phase carbonylation of methanol, andincreased rates are observed when hydrogen is added to the feed mixture.Relevant references to the nickel-on-carbon catalyst systems areprovided by Fujimoto et al. In Chemistry Letters (1987) 895-898 and inJournal of Catalysis, 133 (1992) 370-382 and in the references containedtherein. Liu et al., in Ind. Eng. Chem. Res., 33 (1994) 488-492, reportthat tin enhances the activity of the nickel-on-carbon catalyst. Muelleret al., in U.S. Pat. No. 4,918,218, disclose the addition of palladiumand optionally copper to supported nickel catalysts for thehalide-promoted carbonylation of methanol. In general, the rates ofreaction provided by nickel-based catalysts are lower than thoseprovided by the analogous rhodium-based catalysts when operated undersimilar conditions.

Other single metals supported on carbon have been reported by Fujimotoet al. in Catalysis Letters, 2 (1989) 145-148 to have limited activityin the halide-promoted vapor phase carbonylation of methanol. The mostactive of these metals is Sn. Following Sn in order of decreasingactivity are Pb, Mn, Mo, Cu, Cd, Cr, Re, V, Se, W, Ge and Ga. None ofthese other single metal catalysts are nearly as active as those basedon Rh, Ir, Ni or the catalyst of the present invention.

A number of solid materials have been reported to catalyze thecarbonylation of methanol without the addition of the halide promoter.Gates et al., in Journal of Molecular Catalysis, 3 (1977/78) 1-9,describe a catalyst containing rhodium attached to polymer boundpolychlorinated thiophenol for the liquid phase carbonylation ofmethanol. Current, in European Patent Application EP 0 130 058 A1,describes the use of sulfided nickel containing optional molybdenum as aheterogeneous catalyst for the conversion of ethers, hydrogen and carbonmonoxide into homologous esters and alcohols.

Smith et al., in European Patent Application EP 0 596 632 A1, describethe use of mordenite zeolite containing Cu, Ni, Ir, Rh, or Co ascatalysts for the halide-free carbonylation of alcohols. Feitler, inU.S. Pat. No. 4,612,387, describes the use of certain zeolitescontaining no transition metals as catalysts for the halide-freecarbonylation of alcohols and other compounds in the vapor phase.

U.S. Pat. No. 5,218,140 to Wegman describes a vapor phase process forconverting alcohols and ethers to carboxylic acids and esters by thecarbonylation of alcohols and ethers with carbon monoxide in thepresence of a metal ion exchanged heteropoly acid supported on an inertsupport. The catalyst used in the reaction includes a polyoxometalateanion in which the metal is at least one of a Group V(a) and VI(a) iscomplexed with at least one Group VIII cation such as Fe, Ru, Os, Co,Rh, Ir, Ni, Pd or Pt as catalysts for the halide-free carbonylation ofalcohols and other compounds in the vapor phase. The general formula ofa preferred form of the heteropoly acid used in the practice of theprocess is M[Q₁₂PO₄₀] where M is a Group VIII metal or a combination ofGroup VIII metals, Q is one or more of tungsten, molybdenum, vanadium,niobium, chromium, and tantalum, P is phosphorous and O is oxygen.

The catalyst used in this invention differs from that described in U.S.Pat. No. 5,218,140 in that the group 5 element is not part of aheteropoly acid, that is, the group 5 element employed in the catalystof Wegman is constrained to a heteropoly anion on the preferred supportof silica. Moreover, Wegman does not use a co-catalyst halide. As aconsequence of these differences, the process of the current inventionoperates at a rate greater than about 100 times that described in U.S.Pat. No. 5,218,140.

Certain disadvantages of the prior art carbonylation processes includecatalyst instability, lack of product selectivity, and in liquid phaseprocesses, the need for large and costly recovery equipment andprocedures. Moreover, in liquid phase systems, additional processingsteps are necessary for separation of reaction products from thecatalyst solutions, catalyst recovery and catalyst recycle tocarbonylation reaction zone. A further disadvantage is that there arealways handling losses of the catalyst.

Accordingly, there is a need for a carbonylation process for producingcarboxylic acids and their esters in which the reactants and productsare maintained in the vapor-phase. There is still a further need for acarbonylation process where the reaction is effected by a solid phasecatalyst.

SUMMARY OF THE INVENTION

Briefly, the present invention relates to a method for producing estersand carboxylic acids from lower alkyl alcohols, ethers and ester-alcoholmixtures using vapor-phase carbonylation. The method includes contactingthe reactants, i.e., the lower alkyl alcohols, ethers and ester-alcoholmixtures, with a heterogeneous catalyst. The catalyst includes aneffective amount of iridium and at least one second metal selected fromgroup 5 metals of the periodic table of the elements, their respectivesalts and mixtures thereof. The iridium and at least one second metalselected from vanadium, niobium, tantalum are associated with a solidsupport material which, desirably, is inert to the carbonylationreaction.

It is an object of the invention to provide a method for producingesters and carboxylic acids from lower alkyl alcohols, ethers, andester-alcohol mixtures using vapor phase carbonylation. Moreparticularly, it is an object of the present invention to provide amethod for producing acetic acid, methyl acetate and mixtures thereoffrom lower alkyl alcohols and preferably, methanol using vapor-phasecarbonylation.

It is another object of the invention to provide a process in which thecatalyst is maintained in a solid phase to reduce or eliminate thehandling losses of the catalyst.

It is another object of the invention to provide a vapor phasecarbonylation process for producing acetic acid and methyl acetate whichutilizes a more stable catalyst and reduces the need for catalystrecovery and recycle as well as solvent recovery.

These and other objects and advantages of the invention will becomeapparent to those skilled in the art from the accompanying detaileddescription.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the invention, a method for the continuous productionof carboxylic acids and esters is provided and includes the reacting amixture of lower alkyl alcohols, ethers and ester-alcohol mixtures,carbon monoxide and a halide in the presence of a solid supportedcatalyst and under vapor-phase carbonylation conditions. The solidsupported catalyst includes an effective amount of iridium and at leastone second metal selected from the group consisting of group 5(vanadium, niobium, tantalum) metals of the periodic table of theelements, their respective salts and mixtures thereof associated with asolid support material. In a preferred embodiment, the method providesfor the continuous production of acetic acid, methyl acetate or mixturesthereof by reacting methanol, carbon monoxide and a halide selected fromhydrogen iodide, alkyl and aryl iodides having up to 12 carbon atomsselected from the group consisting of methyl iodide, ethyl iodide,1-iodopropane, 2-iodobutane, 1-iodobutane, benzyl iodide, hydrogenbromide, methyl bromide and mixtures thereof in the presence of a solidsupported catalyst and under vapor-phase carbonylation conditions.

The process of this invention is operated in the vapor phase and,therefore, is practiced at temperatures above the dew point of theproduct mixture, i.e., the temperature at which condensation occurs.However, since the dew point is a complex function of dilution(particularly with respect to non-condensable gases such as unreactedcarbon monoxide, hydrogen, or inert diluent gas), product composition,and pressure, the process may still be operated over a wide range oftemperatures, provided the temperature exceeds the dew point of theproduct effluent. In practice, this generally dictates a temperaturerange of about 100° C. to 500° C., with temperatures in the range of100° C. to 325° C. being preferred and temperature of about 150° C. to275° C. being particularly useful. Advantageously, operating in thevapor phase eliminates catalyst dissolution, i.e., metal leaching fromthe catalyst support, which occurs in the known heterogeneous processesoperating in the presence of liquid compounds.

As with temperature, the useful pressure range is limited by the dewpoint of the product mixture. However, provided that the reaction isoperated at a temperature sufficient to prevent liquefaction of theproduct effluent, a wide range of pressures may be used, e.g., pressuresin the range of about 0.1 to 100 bars absolute. The process preferablyis carried out at a pressure in the range of about 1 to 50 barsabsolute, most preferably, about 3 to 30 bar absolute.

Suitable feed stocks for carbonylation include lower alkyl alcohols,ethers, esters, and ester-alcohol mixtures which may be carbonylatedusing the catalyst of the present invention. Non-limiting examples offeed stocks include alcohols and ethers in which an aliphatic carbonatom is directly bonded to an oxygen atom of either an alcoholichydroxyl group in the compound or an ether oxygen in the compound andmay further include aromatic moieties. Preferably, the feed stock is oneor more lower alkyl alcohols having from 1 to 10 carbon atoms andpreferably having from 1 to 6 carbon atoms, alkane polyols having 2 to 6carbon atoms, alkyl alkylene polyethers having 3 to 20 carbon atoms andalkoxyalkanols having from 3 to 10 carbon atoms. The most preferredreactant is methanol. Although methanol is the preferred feed stock touse with the solid supported catalyst of the present invention and isnormally fed as methanol, it can be supplied in the form of acombination of materials which generate methanol. Examples of suchmaterials include (i) methyl acetate and water and (ii) dimethyl etherand water. During carbonylation, both methyl acetate and dimethyl etherare formed within the reactor and, unless methyl acetate is the desiredproduct, they are recycled with water to the reactor where they areconverted to acetic acid. Accordingly, one skilled in the art willfurther recognize that it is possible to utilize the catalyst of thepresent invention to produce a carboxylic acid from an ester feedmaterial.

The presence of water in the gaseous feed mixture is not essential whenusing methanol, the presence of some water is desirable to suppressformation of methyl acetate and/or dimethyl ether. When using methanolto generate acetic acid, the molar ratio of water to methanol can be 0:1to 10:1, but preferably is in the range of 0.01:1 to 1:1. When using analternative source of methanol such as methyl acetate or dimethyl ether,the amount of water fed usually is increased to account for the mole ofwater required for hydrolysis of the methanol alternative. Accordingly,when using either methyl acetate or dimethyl ether, the mole ratio ofwater to ester or ether is in the range of 1:1 to 10:1, but preferablyin the range of 1:1 to 3:1. In the preparation of acetic acid, it isapparent that combinations of methanol, methyl ester, and/or dimethylether are equivalent, provided the appropriate amount of water is addedto hydrolyze the ether or ester to provide the methanol reactant.

When the vapor phase carbonylation process is operated to produce methylacetate, no water should be added and dimethyl ether becomes thepreferred feed stock. Further, when methanol is used as the feed stockin the preparation of methyl acetate, it is necessary to remove water.However, the primary utility of the catalyst of the present invention isin the manufacture of acetic acid.

The solid supported catalyst has an effective amount of iridiumassociated with a solid support material and at least one second metalselected from the group consisting of vanadium, niobium, tantalum metalsof the periodic table of the elements, their respective salts andmixtures thereof.

The compound or form of iridium used to prepare the solid supportedcatalyst generally is not critical, and the catalyst may be preparedfrom any of a wide variety of iridium containing compounds. Indeed,iridium compounds containing combinations of halide, trivalent nitrogen,organic compounds of trivalent phosphorous, carbon monoxide, hydrogen,and 2,4-pentane-dione, either alone or in combination. Such materialsare available commercially and may be used in the preparation of thecatalysts utilized in the present invention. In addition, the oxides ofiridium may be used if dissolved in the appropriate medium. Preferablyiridium is a salt of one of its chlorides, such as iridium trichlorideor hydrated trichloride, hexacholoro-iridate and any of the varioussalts of hexachloroiridate (IV). One skilled in the art will understandthat use of the preferred iridium complexes should be comparable on thebasis of cost, solubility; and performance.

The solid supported catalyst may be prepared using any of a wide varietyof compounds containing vanadium, niobium, and tantalum, theirrespective salts and mixtures thereof. Desirably, the second metalcompound is selected from halides, oxides, sulfates, nitrates,alkoxides, cyclopentadiene, and 2,4-pentane-dione of the metals, eitheralone or in combination. These compounds are commercially available andmay be used in the preparation of the catalysts used in the process ofthe present invention. The oxides of these materials may be used ifdissolved in the appropriate medium. Desirably, the compound used toprovide the second metal is a water soluble form of the metal(s).Preferred sources include the oxides, nitrates, and their halides. Themost preferred source among these salts would be dictated by itssolubility, preferably water solubility, which can vary widely acrossthis list of useful second components. The most preferred secondarymetals include vanadium, niobium, their salts, or combinations thereof.Salts of the oxides, fluorides, or chlorides of such preferred secondarymetals are generally is commercially available and water soluble, withthe ammonium salts of the complexes being particularly useful in thisrespect.

The solid support useful for acting as a carrier for the iridium and atleast one secondary metal consists of a porous solid of such size thatit can be employed in fixed or fluidized bed reactors. Typical supportmaterials have a size of from about 400 mesh per inch to about ½ inch.Preferably, the support is carbon, including activated carbon, having ahigh surface area, Activated carbon is well known in the art and may bederived from coal or peat having a density of from about 0.03grams/cubic centimeter (g/cm³) to about 2.25 g/cm³. The carbon can havea surface area of from about 200 square meters/gram (m²/g) to about 1200m²/g. Other solid support materials may be used, either alone or incombination, in accordance with the present invention include pumice,alumina, silica, silica-alumina, magnesia, diatomaceous earth, bauxite,titania, zirconia, clays, magnesium silicate, silicon carbide, zeolites,and ceramics. The shape of the solid support is not particularlyimportant and can be regular or irregular and include extrudates, rods,balls, broken pieces and the like disposed within the reactor.

The amount of iridium and secondary metal on the support can vary fromabout 0.01 weight percent to about 10 weight percent, with from about0.1 weight percent to about 2 weight percent of each component beingpreferred.

The preparation of the solid support catalyst is carried out bypreferably dissolving or dispersing the iridium and secondary metalcomponent in a suitable solvent. The solid support material is thencontacted with the iridium and secondary metal containing solutions.Desirably, the iridium and secondary metal are associated with thesupport material as a result of soluble impregnation of the iridium andthe secondary metal which may result in either a salt of the iridiumand/or metals, an oxide of the iridium and/or metals, or as a free metaldeposited on the support. Various methods of contacting the supportmaterial with the iridium and secondary metal may be employed. Forexample, an iridium containing solution can be admixed with a secondarymetal solution prior to impregnating the support material.Alternatively, the respective solutions can be impregnated separatelyinto or associated with the support material prior to impregnating thesupport material with the second solution. For example, the secondarymetal component may be deposited on a previously prepared catalystsupport having the iridium component already incorporated thereon.Desirably, in this alternative embodiment, the support is dried prior tocontacting the second solution. Similarly, the iridium and secondarymetal(s) may be associated with the support material in a variety offorms. For example, slurries of the iridium and at least one secondarymetal can be poured over the support material. Alternatively, thesupport material may be immersed in excess solutions of the activecomponents with the excess being subsequently removed using techniquesknown to those skilled in the art. The solvent or liquid is evaporated,i.e. the solid support is dried so that at least a portion of theiridium and secondary metal is associated with the solid support. Dryingtemperatures can range from about 100° C. to about 600° C. One skilledin the art will understand that the drying time is dependent upon thetemperature, humidity, and solvent. Generally, lower temperaturesrequire longer heating periods to effectively evaporate the solvent fromthe solid support.

The liquid used to deliver the iridium and the secondary metal in theform a solution, dispersion, or suspension is a liquid having a lowboiling point, i.e., high vapor pressure at a temperature of from about10° C. to about 140° C. Examples of suitable solvents include carbontetrachloride, benzene, acetone, methanol, ethanol, isopropanol,isobutanol, pentane, hexane, cyclohexane, heptane, toluene, pyridine,diethylamnine, acetaldehyde, acetic acid, tetrahydrofuran andpreferably, water.

In carrying out the present invention, a gaseous mixture having loweralkyl alcohols, esters, ethers, and other derivatives of the desiredalcohol feedstock; carbon monoxide and a halide promoter are fed to acarbonylation reactor in a vaporous state and contacted with the iridiumand secondary metal supported catalyst described above. The term,“halide” is used generically and interchangeably herein with “halogen”,“halide” or “halide containing compound” and includes both the singularor plural forms. The halide promoter may be introduced at the catalystpreparation step or preferably, is introduced into the carbonylationreactor with the reactants. As a result of contacting the active metalcomponents with the halide promoter the ultimate active species of theiridium and secondary metal may exist as one or more coordinationcompounds or a halide thereof. The reactor is maintained undercarbonylation conditions of temperature and pressure so that thereactants remain in a vaporous state. The process may be operated toproduce high proportions of the carboxylic acid or the ester of thecarboxylic acid. If acetic acid is the desired product, the feed stockmay consist of methyl alcohol, dimethyl ether, methyl acetate, a methylhalide or any combination thereof. If it is desired to increase theproportion of acid produced, the ester may be recycled to the reactortogether with water or introduced into a separate reactor with water toproduce the acid in a separate zone.

The carbon monoxide can be a purified carbon monoxide or include othergases. The carbon monoxide need not be of a high purity and may containfrom about 1% by volume to about 99% by volume carbon monoxide, andpreferably from about 70% by volume to about 99% by volume carbonmonoxide. The remainder of the gas mixture including such gases asnitrogen, hydrogen, carbon dioxide, water and paraffinic hydrocarbonshaving from one to four carbon atoms. Although hydrogen is not part ofthe reaction stoichiometry, hydrogen may be useful in maintainingoptimal catalyst activity. The preferred ratio of carbon monoxide tohydrogen generally ranges from about 99:1 to about 2:1, but ranges witheven higher hydrogen levels are also likely to be useful.

The halide component of the feed includes one or more compoundscontaining chlorine, bromine and/or iodine and preferably, includesbromine and/or iodine which are vaporous under vapor-phase carbonylationconditions of temperature and pressure. Suitable halides includehydrogen halides such as hydrogen iodide and gaseous hydriodic acid;alkyl and aryl halides having up to 12 carbon atoms such as, methyliodide, ethyl iodide, 1-iodopropane, 2-iodobutane, 1-iodobutane, methylbromide, ethyl bromide, and benzyl iodide. Desirably, the halide is ahydrogen halide or an alkyl halide having up to 6 carbon atoms.Non-limiting examples of preferred halides hydrogen iodide, methylbromide and methyl iodide. The halide may also be a molecular halidesuch as I₂, Br₂, or Cl₂.

The amount of halide present to produce an effective carbonylationranges from a molar ratio of about 1:1 to 10,000:1, of methanol ormethanol equivalents to halide with the preferred range being from about5:1 to about 1000:1.

In a preferred aspect of the invention, the vapor-phase carbonylationcatalyst of the present invention may be used for making acetic acid,methyl acetate or a mixture thereof. is The process includes the stepsof contacting a gaseous mixture comprising methanol and carbon monoxidewith the iridium/secondary metal catalyst described above in acarbonylation zone and recovering a gaseous product from thecarbonylation zone.

The present invention is illustrated in greater detail by the specificexamples present below. It is to be understood that these examples areillustrative embodiments and are not intended to be limiting of theinvention, but rather are to be construed broadly within the scope andcontent of the appended claims.

In the examples which follow all of the catalysts were prepared in asimilar manner and run under similar conditions unless specifiedotherwise.

Catalyst 1

A catalyst in accordance with the present invention containing vanadiumand iridium was prepared as follows:

Ammonium metavanadate (0.136 grams, 1.16 mmol) was dissolved in 30 mL ofdistilled water at 50° C. The solution was then added to 20 grams of12×40 mesh activated carbon granules obtained from CALGON and having aBET surface area in excess of 800 m²/g. The mixture was heated in anevaporating dish using a steam bath and continuously stirred until thegranules became free flowing. The free flowing granules were transferredto a quartz tube measuring 106 centimeters (cm) long and having anoutside diameter of about 25 millimeters (mm). The packed quartz tubecontaining the mixture was placed in a three-element electric tubefurnace so that the mixture was located in the approximate center of the61 cm long heated zone of the furnace. Nitrogen at a rate of 100standard cubic centimeters per minute was continuously passed throughthe catalyst bed, while the packed tube was heated from ambienttemperature to 300° C. over a 2 hour period, held at 300° C. for 2 hoursand then allowed to cool back to ambient temperature. This vanadium onactivated carbon was removed from the quartz tube and used in subsequentsteps.

Iridium (III) chloride hydrate (0.412 g, 1.16 mmol) was dissolved in 30mL of distilled water and the solution was then added to a portion ofthe vanadium on activated carbon granules (from above) in an evaporatingdish. The mixture was heated using a steam bath and continuously stirreduntil it became free flowing. The free flowing granules were transferredto a quartz tube measuring 106 centimeters (cm) long and having anoutside diameter of about 25 millimeters (mm). The packed quartz tubecontaining the mixture was placed in a three-element electric tubefurnace so that the mixture was located in the approximate center of the61 cm long heated zone of the furnace. Nitrogen at a flow rate of 100standard cubic centimeters per minute was continuously passed throughthe catalyst bed, and the tube was heated from ambient temperature to300° C. over a 2 hour period, held at 300° C. for 2 hours and thenallowed to cool back to ambient temperature. The catalyst contained0.30% vanadium, 1.12% iridium and had a density of 0.57 g/mL.

Comparative Catalyst A

For Comparative Catalyst A, the vanadium on activated carbon prepared inCatalyst 1 above was used. Catalyst A contained 0.30% vanadium and had adensity of 0.57 g/mL.

Comparative Catalyst B

For Comparative Catalyst B, iridium on an activated carbon support wasprepared as follows:

Iridium (III) chloride hydrate (0.418 g, 1.17 mmol of Ir) was dissolvedin 30 mL of distilled water. The solution was then added to 20 grams of12×40 mesh activated carbon granules obtained from CALGON and having aBET surface area in excess of 800 m²/g. The mixture was heated in anevaporating dish using a steam bath and continuously stirred until thegranules became free flowing. The free flowing granules were transferredto a quartz tube measuring 106 centimeters (cm) long and having anoutside diameter of about 25 millimeters (mm). The packed quartz tubecontaining the mixture was placed in a three-element electric tubefurnace so that the mixture was located in the approximate center of the61 cm long heated zone of the furnace. Nitrogen at a flow rate of 100standard cubic centimeters per minute was continuously passed throughthe catalyst bed, and the tube was heated from ambient temperature to300° C. over a 2 hour period, held at 300° C. for 2 hours and thenallowed to cool back to ambient temperature. Catalyst B contained 1.10%Ir and had a density of 0.57 g per mL.

Catalyst 2

A second catalyst in accordance with the present invention containingniobium and iridium was prepared as follows:

The methodology used to prepare Catalyst 1 was repeated, except thatammonium hexafluoroniobate (V) (0.262 grams, 1.16 mmol) was used inplace of ammonium metavanadate. Dissolution of ammoniumhexafluoroniobate (v) was accomplished at room temperature and did notrequire heating. Catalyst 2 contained 0.54% Nb, 1.12% Ir, and had adensity of 0.57 g/mL.

Comparative Catalyst C

For Comparative Catalyst C, niobium on an activated carbon support wasprepared as follows:

The methodology used to prepare Comparative Catalyst B was repeated,except that ammonium hexafluoroniobate (V) (0.262 grams, 1.16 mmol) wasused in place of iridium (III) chloride hydrate. Comparative Catalyst Ccontained 0.54% Nb and had a density of 0.57 g/mL.

Catalyst 3

A third catalyst in accordance with the present invention containingtantalum and iridium was prepared as follows:

The methodology used to prepare Catalyst 1 was repeated, except thatammonium hexafluorotantalate (V) (0.408 grams, 1.16 mmol) was used inplace of ammonium metavanadate. Dissolution of ammoniumhexafluorotantalate (V) was accomplished at room temperature and did notrequire heating. Catalyst 3 contained 0.96% Ta and 1.01% Ir by analysisand had a density of 0.57 g/mL.

Comparative Catalyst D

For Comparative Catalyst D, tantalum on an activated carbon support wasprepared as follows:

The methodology used to prepare Comparative Catalyst B was repeated,except that ammonium hexafluorotantalate (V) (0.408 grams, 1.16 mmol)was used in place of iridium (III) chloride hydrate. Dissolution ofammonium hexafluorotantalate (V) was accomplished at room temperatureand did not require heating to 50° C. Catalyst D contained 0.97% Ta byanalysis and had a density of 0.57 g/mL.

Carbonylation of Methanol

The reactor system consisted of a 800 to 950 mm (31.5 and 37 inch)section of 6.35 nm (¼ inch) diameter tubing constructed of Hastelloyalloy. The upper portion of the tube constituted the preheat andreaction (carbonylation) zones which were assembled by inserting aquartz wool pad 410 mm from the top of the reactor to act as support forthe catalyst, followed sequentially by (1) a 0.7 gram bed of fine quartzchips (840 microns), (2) 0.5 gram of one of the catalysts prepared asdescribed in the preceding examples, and (3) an additional 6 grams offine quartz chips. The top of the tube was attached to an inlet manifoldfor introducing liquid and gaseous feeds.

The six grams of fine quartz chips acted as a heat exchange surface tovaporize the liquid feeds. Care was taken not to allow any liquid feedsto contact the catalyst bed at any time, including assembly, start-up,operation, and shutdown. The remaining lower length of tubing (productrecovery section) consisted of a vortex cooler which varied in lengthdepending on the original length of tubing employed and was maintainedat approximately 0-5° C. during operation.

The gases were fed using Brooks flow controllers and liquids were fedusing a high performance liquid chromatography pump. The gaseousproducts leaving the reaction zone were condensed using a vortex cooleroperating at 0-5° C. The product reservoir was a tank placed downstreamfrom the reactor system. The pressure was maintained using a Tescom44-2300 Regulator on the outlet side of the reactor system and thetemperature of the reaction section was maintained using heating tape onthe outside of the reaction system.

Feeding of hydrogen and carbon monoxide to the reactor was commencedwhile maintaining the reactor at a temperature of 240° C. and a pressureof 17.2 bara (250 psia). The flow rate of hydrogen was set at 25standard cubic cm. per minute (cc/min) and the carbon monoxide flow ratewas set at 100 cc/min. The reactor section was maintained under theseconditions for 1 hour or until the temperature and pressure hadstabilized (whichever was longer.) The high pressure liquidchromatography pump was then started, feeding a mixture consisting of 70weight percent methanol and 30 weight percent methyl iodide at a rate of12 ml/min (The solution had a density of 1 g/mL.) Samples of the liquidproduct were collected and analyzed periodically using gaschromatographic techniques.

Carbonylation Example 1

The composition and weight of the samples taken periodically during theprocedure described above in which Catalyst 1 was used are set forth inTable 1 wherein “Time” is the total time of operation (in hours) of thecarbonylation commencing with the feeding of the methanol until aparticular sample was taken. The values set forth below “MeI” (methyliodide), “MeOAc” (methyl acetate), “MeOH” (methanol) and “HOAc” (aceticacid) are the weight percentages of each of those compounds present inthe sample. The weight of each sample is given in grams.

TABLE 1 Expired Sample Sample Time MeI MeOAc MeOH HOAc Weight No. (hr.)(Wt. %) (Wt. %) (Wt. %) (Wt. %) (g)  1  3.00 22.52 21.88 1.56 43.25 37.9 2  7.00 22.13 21.32 1.55 43.24 49.1  3 10.00 21.67 21.65 1.79 44.0437.2  4 15.00 22.04 21.16 1.6  42.39 62.1  5 17.00 22.59 21.4  1.5242.64 25.1  6 23.00 23.31 18.76 0.79 45.19 72.3  7 27.00 23.23 18.861.09 46.26 49.1  8 31.00 23.16 18.84 0.89 45.45 48.5  9 34.00 21.2919.03 1.32 47.58 37.3 10 39.00 20.91 18.8  1.14 46.73 60.1 11 41.0020.96 19.41 1.45 47.8  25.6 12 47.00 20.8  18.88 0.88 49.21 71.9 1351.00 21.19 18.42 1.03 48.43 48.2 14 55.00 20.87 18.6  0.99 49.14 48.915 58.00 20.47 18.52 0.8  50.02 37.1 16 63.00 20.35 18.59 0.72 50.0361.1 17 65.00 19.94 18.58 0.85 50.69 26.2 18 71.00 11.59 20.83 1.9852.99 73.2 19 75.00 18.88 18.85 0.97 50.99 49.1 20 79.00 19.51 18.440.87 50.67 48.9

The rate of acetyl production based on the preceding experimentutilizing Catalyst 1 is set forth in Table 2 below. The Sample Numberand Time values correspond to those of Table 1. “Acetyl Produced”represents the quantity, in millimoles, of methyl acetate and aceticacid produced during each increment of Time. Acetyl Produced iscalculated from the formula:

Acetyl Produced=(Sample weight (grams))×10×((weight % ofMeOAc/74)+(weight % of AcOH/60)).

“Production Rate” is the moles of Acetyl Produced per liter of catalystvolume per hour during each increment of Time (Time Increment), i.e.,the time of operation between samples. The formula for determining molesof Acetyl Produced per liter of catalyst volume per hour (space timeyield) is determined as follows:$\frac{\text{((density~~~of~~~the~~~catalyst~~(g/ml))} \times ( {{Acetyl}\quad {Produced}} )\text{)}}{( {( {{grams}\quad {of}\quad {catalyst}\quad {used}} ) \times ( {{Time}\quad {Increment}} )} )}$

TABLE 2 Acetyl Sample Produced Rate No. (mmol) (mol/L-h)  1 385.3 146.4 2 495.3 141.2  3 381.9 145.1  4 616.3 140.5  5 251.0 143.0  6 727.8138.3  7 503.7 143.6  8 490.9 139.9  9 391.7 148.8 10 620.8 141.5 11271.1 154.5 12 773.1 146.9 13 509.0 145.1 14 523.4 149.2 15 402.1 152.816 663.0 151.2 17 287.1 163.7 18 852.5 162.0 19 542.3 154.6 20 534.8152.4

During the 79 hours of testing, the catalyst produced 10.22 moles ofacetyl. This represents a rate of 259 moles of acetyl per kilogram ofcatalyst per hour (acetyl/kg_(cat)-h) or, represented as a space timeyield, 147 mol of acetyl/L_(cat)-h.

Carbonylation Using Catalyst 2-3 and Comparative Catalysts A-D

Catalyst 2-3 and comparative Example Catalysts A-D were used in thecarbonylation of methanol using the same procedure and parameters asdescribed above. The Production Rate, expressed in terms of moles ofAcetyl Produced per kilogram of catalyst per hour and moles per liter ofcatalyst volume per hour, for each of the catalysts is shown in Table 3below.

TABLE 3 Carbonylation Production Rate Example Catalyst moles/kg_(cat)-hmoles/L_(cat)-h 1 1 259  147  CE-1 A 13  7 CE-2 B 93 53 2 2 244  139 CE-3 C 26 15 3 3 146  83 CE-4 D 61 35

As can be seen from Table 3, a carbonylation catalyst having iridium andat least one metal from the group 5 (V, Nb, Ta) produces exceptionallyand quite unexpectedly, very high rates of acetyl production.

Although the present invention has been shown and described in terms ofthe presently preferred embodiment(s), it is to be understood thatvarious modifications and substitutions, rearrangements of parts,components and process steps can be made by those skilled in the artwithout departing from the novel spirit and scope of the invention.

We claim:
 1. A method for producing esters and carboxylic acids fromreactants comprising lower alkyl alcohols, ethers, esters andester-alcohol mixtures, said method comprising contacting a vaporousmixture comprising the reactants, carbon monoxide and a halide with asupported catalyst in a carbonylation zone of a carbonylation reactorand under vapor-phase conditions, wherein said catalyst consistsessentially of an effective amount of iridium and a second metalselected from the group consisting of vanadium, niobium, tantalum, theirrespective salts and mixtures thereof, and wherein said iridium and saidsecond metal are associated with a solid catalyst support material. 2.The method of claim 1 wherein said reactants are selected from the groupconsisting of lower alkyl alcohols having from 1 to 10 carbon atoms,alkane polyols having 2 to 6 carbon atoms, alkyl alkylene polyethershaving 3 to 20 carbon atoms and alkoxyalkanols having from 3 to 10carbon atoms and mixtures thereof.
 3. The method of claim 1 wherein saidreactant is methanol.
 4. The method of claim 1 wherein said reactant isdimethyl ether.
 5. The method of claim 1 wherein esters and carboxylicacids produced from said vapor phase carbonylation include acetic acid,methyl acetate and mixtures thereof.
 6. The method of claim 1 whereinsaid halide is selected from the group consisting of chloride, bromide,iodide and mixtures thereof.
 7. The method of claim 6 wherein saidwherein said halide is selected from the group consisting of hydrogeniodide, gaseous hydriodic acid; alkyl and aryl iodides having; up to 12carbon atoms selected from the group consisting of methyl iodide, ethyliodide, 1-iodopropane, 2-iodobutane, 1-iodobutane, benzyl iodide,hydrogen bromide, methyl bromide and mixtures thereof.
 8. The method ofclaim 7 wherein said halide is selected from the group consisting ofiodine, hydrogen iodide, methyl iodide, bromine, hydrogen bromide,methyl bromide and mixtures thereof.
 9. The method of claim 1 whereinsaid carbonylation zone is maintained at a temperature of about 100° C.to 350° C. and a pressure of about 1 to 50 bar absolute.
 10. The methodof claim 1 wherein said solid support is selected from carbon, activatedcarbon, pumice, alumina, silica, silica-alumina, magnesia, diatomaceousearth, bauxite, titania, zirconia, clays, magnesium silicate, siliconcarbide, zeolites, and ceramics, wherein said support has a surface areafrom about 200 m²/g to about 1200 m²/g.
 11. The method of claim 1wherein said catalyst includes from about 0.01 weight percent to about10 weight percent each of iridium and said second metal.
 12. The methodof claim 1 wherein said catalyst includes from about 0.1 weight percentto about 2 weight percent each of iridium and said second metal.
 13. Themethod of claim 3 wherein the gaseous reactants further includes waterin an amount which gives a water to methanol mole ratio of about 0.01:1to 1:1.
 14. The method of claim 10 wherein said solid support isselected from carbon and activated carbon.
 15. A method for producingacetic acid, methyl acetate or a mixture thereof comprising the stepsof: a. contacting a vaporous mixture comprising methanol, carbonmonoxide, and a halide selected from the group consisting of chlorine,bromine, iodine and mixtures thereof with a supported catalyst undercarbonylation conditions of temperature and pressure of from about 100°to about 350° C. and from about 1 to about 50 bar absolute, wherein saidcatalyst consists essentially of an effective amount of iridium and asecond metal selected from the group consisting of vanadium, niobium,tantalum, their respective salts and mixtures thereof, and wherein saidiridium and said second metal are associated with a solid catalystsupport material selected from the group consisting of carbon, activatedcarbon, silica, silica-alumina, zirconia, clays, magnesium silicate,silicon carbide, zeolites, and mixtures thereof; and b. recoveringacetic acid, methyl acetate or a mixture thereof from the vaporousproduct.
 16. The vapor-phase carbonylation method of claim 15 whereinsaid secondary metal is selected from the group consisting of vanadium,niobium, their respective salts and mixtures thereof.
 17. Thevapor-phase carbonylation method of claim 15 wherein said halide isselected from the group consisting of iodine, hydrogen iodide, methyliodide, bromide, hydrogen bromide, methyl bromide and mixtures thereof.18. The vapor-phase carbonylation method of claim 15 wherein saidcatalyst includes from about 0.1 weight percent to about 2 weightpercent each of iridium and said second metal.
 19. A method forproducing acetic acid, methyl acetate or a mixture thereof comprisingthe steps of: a. contacting a vaporous mixture comprising methanol,carbon monoxide, and a halide selected from the group consisting ofiodine, hydrogen iodide, methyl iodide, bromide, hydrogen bromide,methyl bromide and mixtures thereof with an activated carbon supportedcatalyst under carbonylation conditions of temperature and pressure offrom about 150° to about 275° C. and from about 1 to about 50 barabsolute, wherein said catalyst consists essentially of from about 0.1weight % to about 2 weight % of iridium and from about 0.1 weight % toabout 2 weight % of a second metal selected from the group consisting ofvanadium, niobium, tantalum metals of the periodic table of elements,their respective salts and mixtures thereof; and b. recovering aceticacid, methyl acetate or a mixture thereof from the vaporous product. 20.The method of claim 19 wherein acetic acid is the desired product andsaid gaseous mixture further includes at least one of an ester or anether selected from the group consisting of methyl acetate and dimethylether.